OTTAWA - Confessions extracted through so-called Mr. Big police sting operations tend to produce unreliable confessions, are open to abuses and must be presumed inadmissible in court, the Supreme Court of Canada ruled Thursday.

The decision by the country's highest court calls into question the convictions of Canadians behind bars across the country and has the potential to reduce wrongful convictions, say civil rights advocates and legal experts.

It has also caused the Mounties to review their policies, although they are defending the investigative technique.

In a majority decision, the court ruled that stings like the one used to convict a Newfoundland man of drowning his three-year-old twin daughters are fraught with risks.

Nelson Hart was initially convicted of first-degree murder in March 2007 in the drowning deaths of his daughters, Krista and Karen, in 2002. At his trial, court was told that Hart demonstrated for undercover officers, posing as members of the mafia, how he drowned the girls by shoving them into the waters of Gander Lake, in central Newfoundland.

But the conviction was overturned in September 2012 by the province's appeal court by a 2-1 margin. The ruling questioned the reliability of his confession.

On Thursday, the Supreme Court justices ruled that Hart's confession during the sting operation cannot be used against him should he face another trial.

It will now be up to the Crown to determine whether Hart will be retried. Frances Knickle, the Crown attorney on the Hart case, wouldn't comment Thursday, saying the decision is under review.

The Supreme Court ruled that Hart's charter rights may have been violated and that Canada's legal system does not adequately protect the rights of people who are subject to Mr. Big sting operations.

In its judgment, the court said that prosecutors must prove a Mr. Big confession is admissible by showing it's reliable, and that it won't unfairly prejudice a crime suspect during court proceedings. The Crown must also prove the confession was not obtained via police coercion, or was facilitated due to a suspect's mental health or addiction issues.

The Mr. Big investigative technique involves undercover police officers who recruit a suspect to a fictitious criminal organization while posing as gangsters. The aim is to obtain a confession to a crime.

He praised the Supreme Court for making it much more difficult for law enforcement agencies to employ Mr. Big stings, but suggested the justices should have outlawed such procedures outright.

"I wish there was an absolute bar to this sort of stuff — the risk of wrongful convictions is just too great — but ultimately the Supreme Court balked at that because this court has a lot of reverence for police investigations," Russomanno said in an interview.

But he added the judgment could give police pause in future investigations if they're pondering a Mr. Big-type sting.

"Let's hope that police forces are going to be a lot more reluctant to engage in it knowing they'll have to spend a lot of money on what could turn out to be a fruitless exercise, and Crown attorneys will not want to lead that kind of evidence," he said.

Lisa Dufraimont, a law professor at Queen's University, called the decision far-reaching.

"It's a very powerful statement to say that Mr. Big confessions are presumptively inadmissible and that the Crown is going to have to establish their admissibility," she said in an interview.

"It certainly gives defence lawyers a much stronger starting point when dealing with Mr. Big confessions. It will have the effect into the future of making the police much more careful about the kinds of tactics that they do engage in."

There are indeed "significant problems" with Mr. Big stings, the Supreme Court ruled.

"To be sure, Mr. Big operations can become abusive, and they can produce confessions that are unreliable and prejudicial," the court said. "We must seek a legal framework that protects accused persons, and the justice system as a whole, against these dangers."

The court added: "Mr. Big operations are a creative and sometimes useful law enforcement technique, but the courts must carefully police their boundaries lest they stray from being useful strategies into ploys that allow the state to manipulate and destroy the lives of individuals who are presumed to be innocent."

The RCMP said it would review the decision to see how it will affect future investigations.

The Association in Defence of the Wrongly Convicted predicted the ruling will help spare innocent people from being falsely accused, tried and convicted.

The B.C. Civil Liberties Association also lauded the decision.

"The risk of wrongful conviction associated with the use of unreliable and prejudicial statements cannot be understated," Carmen Cheung, senior counsel at the association, said in a statement.

"We hope that the court's decision today will help ensure the reliability of evidence in criminal proceedings and help rein in some of the more abusive aspects of Mr. Big operations."

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